The present invention relates generally to beads, methods of making beads, and methods of using beads to remove metal and other ionic contaminants dissolved in aqueous solutions. The beads preferably include activated carbon and a binder and the activated carbon, and preferably the binder, are capable of sorbing dissolved metal ions.
The removal of metal contaminants from aqueous wastes such as acid mine drainage/water and industrial waste water such as metal finishing waste water and municipal waste water, is an important environmental and economic issue. Some of the metal ions are toxic and some are valuable. In the chemical area of toxic metal recovery from dilute aqueous steams, the techniques of recovery have most commonly been by chemical precipitation, ion exchange, reverse osmosis, electrodialysis, solvent extraction (liquid ion exchange), and chemical reduction. (See U.S. Pat. No. 5,279,245). However, these procedures are characterized by the disadvantages of incomplete metal removal, high reagent and energy requirements, and generation of toxic sludge or other waste products that must be disposed of, and these disadvantages are particularly conspicuous at the low metal concentrations often encountered in waste waters, where federally-mandated cleanup standards dictate that effluents discharged to public waters generally contain less than 1 mg/L of metals such as copper, zinc, cadmium, lead, mercury and manganese.
Thus there exists a need for a more effective metal ion sorbent immobilized in a matrix in a mechanical shape such as a bead and for an effective, less-hazardous method of making such beads using binders or matrix materials which do not involve hazardous materials. Preferably the binder or matrix material itself is capable of sorbing The sorbent should be able to remove contaminants from both wastewater and potable water. There is a further need for a process which makes beads which are uniformly spheroidal. Non-spheroidal beads tend to pack asymmetrically, tending to cause water flowing there-through to flow in certain channels, rather than uniformly over all the beads. Among the objects of the present invention are to answer these needs.
A bead is provided which comprises activated carbon and a binder, the binder preferably being poly(carboxylic acid) effectively crosslinked with a crosslinking agent. The activated carbon is effectively immobilized in the bead. The bead is capable of sorbing a metal or other ions dissolved in a dilute aqueous solution at a concentration of less than 10 ppm, said metal or ion being selected from the group consisting of lead, copper, silver, chromium, cobalt, uranium, mercury, nickel, arsenic, aluminum, cadmium, iron, manganese, and zinc. A method of making a metal-ion-sorbing bead is also provided. The method comprises:
(a) combining, activated carbon, such as bituminous coal-based powdered carbon, and binder solution into a mixture, the binder solution comprising poly(carboxylic acid) and a crosslinking agent;
(b) forming the mixture into a first bead;
(c) heating said first bead to effectively crosslink the poly(carboxylic acid) with the crosslinking agent to form an effectively crosslinked binder.
A method of using the bead for removing a metal or metalloid from a dilute aqueous solution is also provided.